1/*
2 * jcprepct.c
3 *
4 * This file is part of the Independent JPEG Group's software:
5 * Copyright (C) 1994-1996, Thomas G. Lane.
6 * It was modified by The libjpeg-turbo Project to include only code relevant
7 * to libjpeg-turbo.
8 * For conditions of distribution and use, see the accompanying README.ijg
9 * file.
10 *
11 * This file contains the compression preprocessing controller.
12 * This controller manages the color conversion, downsampling,
13 * and edge expansion steps.
14 *
15 * Most of the complexity here is associated with buffering input rows
16 * as required by the downsampler. See the comments at the head of
17 * jcsample.c for the downsampler's needs.
18 */
19
20#define JPEG_INTERNALS
21#include "jinclude.h"
22#include "jpeglib.h"
23
24
25/* At present, jcsample.c can request context rows only for smoothing.
26 * In the future, we might also need context rows for CCIR601 sampling
27 * or other more-complex downsampling procedures. The code to support
28 * context rows should be compiled only if needed.
29 */
30#ifdef INPUT_SMOOTHING_SUPPORTED
31#define CONTEXT_ROWS_SUPPORTED
32#endif
33
34
35/*
36 * For the simple (no-context-row) case, we just need to buffer one
37 * row group's worth of pixels for the downsampling step. At the bottom of
38 * the image, we pad to a full row group by replicating the last pixel row.
39 * The downsampler's last output row is then replicated if needed to pad
40 * out to a full iMCU row.
41 *
42 * When providing context rows, we must buffer three row groups' worth of
43 * pixels. Three row groups are physically allocated, but the row pointer
44 * arrays are made five row groups high, with the extra pointers above and
45 * below "wrapping around" to point to the last and first real row groups.
46 * This allows the downsampler to access the proper context rows.
47 * At the top and bottom of the image, we create dummy context rows by
48 * copying the first or last real pixel row. This copying could be avoided
49 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
50 * trouble on the compression side.
51 */
52
53
54/* Private buffer controller object */
55
56typedef struct {
57 struct jpeg_c_prep_controller pub; /* public fields */
58
59 /* Downsampling input buffer. This buffer holds color-converted data
60 * until we have enough to do a downsample step.
61 */
62 JSAMPARRAY color_buf[MAX_COMPONENTS];
63
64 JDIMENSION rows_to_go; /* counts rows remaining in source image */
65 int next_buf_row; /* index of next row to store in color_buf */
66
67#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
68 int this_row_group; /* starting row index of group to process */
69 int next_buf_stop; /* downsample when we reach this index */
70#endif
71} my_prep_controller;
72
73typedef my_prep_controller *my_prep_ptr;
74
75
76/*
77 * Initialize for a processing pass.
78 */
79
80METHODDEF(void)
81start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
82{
83 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
84
85 if (pass_mode != JBUF_PASS_THRU)
86 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
87
88 /* Initialize total-height counter for detecting bottom of image */
89 prep->rows_to_go = cinfo->image_height;
90 /* Mark the conversion buffer empty */
91 prep->next_buf_row = 0;
92#ifdef CONTEXT_ROWS_SUPPORTED
93 /* Preset additional state variables for context mode.
94 * These aren't used in non-context mode, so we needn't test which mode.
95 */
96 prep->this_row_group = 0;
97 /* Set next_buf_stop to stop after two row groups have been read in. */
98 prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
99#endif
100}
101
102
103/*
104 * Expand an image vertically from height input_rows to height output_rows,
105 * by duplicating the bottom row.
106 */
107
108LOCAL(void)
109expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
110 int input_rows, int output_rows)
111{
112 register int row;
113
114 for (row = input_rows; row < output_rows; row++) {
115 jcopy_sample_rows(image_data, input_rows-1, image_data, row,
116 1, num_cols);
117 }
118}
119
120
121/*
122 * Process some data in the simple no-context case.
123 *
124 * Preprocessor output data is counted in "row groups". A row group
125 * is defined to be v_samp_factor sample rows of each component.
126 * Downsampling will produce this much data from each max_v_samp_factor
127 * input rows.
128 */
129
130METHODDEF(void)
131pre_process_data (j_compress_ptr cinfo,
132 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
133 JDIMENSION in_rows_avail,
134 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
135 JDIMENSION out_row_groups_avail)
136{
137 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
138 int numrows, ci;
139 JDIMENSION inrows;
140 jpeg_component_info *compptr;
141
142 while (*in_row_ctr < in_rows_avail &&
143 *out_row_group_ctr < out_row_groups_avail) {
144 /* Do color conversion to fill the conversion buffer. */
145 inrows = in_rows_avail - *in_row_ctr;
146 numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
147 numrows = (int) MIN((JDIMENSION) numrows, inrows);
148 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
149 prep->color_buf,
150 (JDIMENSION) prep->next_buf_row,
151 numrows);
152 *in_row_ctr += numrows;
153 prep->next_buf_row += numrows;
154 prep->rows_to_go -= numrows;
155 /* If at bottom of image, pad to fill the conversion buffer. */
156 if (prep->rows_to_go == 0 &&
157 prep->next_buf_row < cinfo->max_v_samp_factor) {
158 for (ci = 0; ci < cinfo->num_components; ci++) {
159 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
160 prep->next_buf_row, cinfo->max_v_samp_factor);
161 }
162 prep->next_buf_row = cinfo->max_v_samp_factor;
163 }
164 /* If we've filled the conversion buffer, empty it. */
165 if (prep->next_buf_row == cinfo->max_v_samp_factor) {
166 (*cinfo->downsample->downsample) (cinfo,
167 prep->color_buf, (JDIMENSION) 0,
168 output_buf, *out_row_group_ctr);
169 prep->next_buf_row = 0;
170 (*out_row_group_ctr)++;
171 }
172 /* If at bottom of image, pad the output to a full iMCU height.
173 * Note we assume the caller is providing a one-iMCU-height output buffer!
174 */
175 if (prep->rows_to_go == 0 &&
176 *out_row_group_ctr < out_row_groups_avail) {
177 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
178 ci++, compptr++) {
179 expand_bottom_edge(output_buf[ci],
180 compptr->width_in_blocks * DCTSIZE,
181 (int) (*out_row_group_ctr * compptr->v_samp_factor),
182 (int) (out_row_groups_avail * compptr->v_samp_factor));
183 }
184 *out_row_group_ctr = out_row_groups_avail;
185 break; /* can exit outer loop without test */
186 }
187 }
188}
189
190
191#ifdef CONTEXT_ROWS_SUPPORTED
192
193/*
194 * Process some data in the context case.
195 */
196
197METHODDEF(void)
198pre_process_context (j_compress_ptr cinfo,
199 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
200 JDIMENSION in_rows_avail,
201 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
202 JDIMENSION out_row_groups_avail)
203{
204 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
205 int numrows, ci;
206 int buf_height = cinfo->max_v_samp_factor * 3;
207 JDIMENSION inrows;
208
209 while (*out_row_group_ctr < out_row_groups_avail) {
210 if (*in_row_ctr < in_rows_avail) {
211 /* Do color conversion to fill the conversion buffer. */
212 inrows = in_rows_avail - *in_row_ctr;
213 numrows = prep->next_buf_stop - prep->next_buf_row;
214 numrows = (int) MIN((JDIMENSION) numrows, inrows);
215 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
216 prep->color_buf,
217 (JDIMENSION) prep->next_buf_row,
218 numrows);
219 /* Pad at top of image, if first time through */
220 if (prep->rows_to_go == cinfo->image_height) {
221 for (ci = 0; ci < cinfo->num_components; ci++) {
222 int row;
223 for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
224 jcopy_sample_rows(prep->color_buf[ci], 0,
225 prep->color_buf[ci], -row,
226 1, cinfo->image_width);
227 }
228 }
229 }
230 *in_row_ctr += numrows;
231 prep->next_buf_row += numrows;
232 prep->rows_to_go -= numrows;
233 } else {
234 /* Return for more data, unless we are at the bottom of the image. */
235 if (prep->rows_to_go != 0)
236 break;
237 /* When at bottom of image, pad to fill the conversion buffer. */
238 if (prep->next_buf_row < prep->next_buf_stop) {
239 for (ci = 0; ci < cinfo->num_components; ci++) {
240 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
241 prep->next_buf_row, prep->next_buf_stop);
242 }
243 prep->next_buf_row = prep->next_buf_stop;
244 }
245 }
246 /* If we've gotten enough data, downsample a row group. */
247 if (prep->next_buf_row == prep->next_buf_stop) {
248 (*cinfo->downsample->downsample) (cinfo,
249 prep->color_buf,
250 (JDIMENSION) prep->this_row_group,
251 output_buf, *out_row_group_ctr);
252 (*out_row_group_ctr)++;
253 /* Advance pointers with wraparound as necessary. */
254 prep->this_row_group += cinfo->max_v_samp_factor;
255 if (prep->this_row_group >= buf_height)
256 prep->this_row_group = 0;
257 if (prep->next_buf_row >= buf_height)
258 prep->next_buf_row = 0;
259 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
260 }
261 }
262}
263
264
265/*
266 * Create the wrapped-around downsampling input buffer needed for context mode.
267 */
268
269LOCAL(void)
270create_context_buffer (j_compress_ptr cinfo)
271{
272 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
273 int rgroup_height = cinfo->max_v_samp_factor;
274 int ci, i;
275 jpeg_component_info *compptr;
276 JSAMPARRAY true_buffer, fake_buffer;
277
278 /* Grab enough space for fake row pointers for all the components;
279 * we need five row groups' worth of pointers for each component.
280 */
281 fake_buffer = (JSAMPARRAY)
282 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
283 (cinfo->num_components * 5 * rgroup_height) *
284 sizeof(JSAMPROW));
285
286 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
287 ci++, compptr++) {
288 /* Allocate the actual buffer space (3 row groups) for this component.
289 * We make the buffer wide enough to allow the downsampler to edge-expand
290 * horizontally within the buffer, if it so chooses.
291 */
292 true_buffer = (*cinfo->mem->alloc_sarray)
293 ((j_common_ptr) cinfo, JPOOL_IMAGE,
294 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
295 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
296 (JDIMENSION) (3 * rgroup_height));
297 /* Copy true buffer row pointers into the middle of the fake row array */
298 MEMCOPY(fake_buffer + rgroup_height, true_buffer,
299 3 * rgroup_height * sizeof(JSAMPROW));
300 /* Fill in the above and below wraparound pointers */
301 for (i = 0; i < rgroup_height; i++) {
302 fake_buffer[i] = true_buffer[2 * rgroup_height + i];
303 fake_buffer[4 * rgroup_height + i] = true_buffer[i];
304 }
305 prep->color_buf[ci] = fake_buffer + rgroup_height;
306 fake_buffer += 5 * rgroup_height; /* point to space for next component */
307 }
308}
309
310#endif /* CONTEXT_ROWS_SUPPORTED */
311
312
313/*
314 * Initialize preprocessing controller.
315 */
316
317GLOBAL(void)
318jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
319{
320 my_prep_ptr prep;
321 int ci;
322 jpeg_component_info *compptr;
323
324 if (need_full_buffer) /* safety check */
325 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
326
327 prep = (my_prep_ptr)
328 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
329 sizeof(my_prep_controller));
330 cinfo->prep = (struct jpeg_c_prep_controller *) prep;
331 prep->pub.start_pass = start_pass_prep;
332
333 /* Allocate the color conversion buffer.
334 * We make the buffer wide enough to allow the downsampler to edge-expand
335 * horizontally within the buffer, if it so chooses.
336 */
337 if (cinfo->downsample->need_context_rows) {
338 /* Set up to provide context rows */
339#ifdef CONTEXT_ROWS_SUPPORTED
340 prep->pub.pre_process_data = pre_process_context;
341 create_context_buffer(cinfo);
342#else
343 ERREXIT(cinfo, JERR_NOT_COMPILED);
344#endif
345 } else {
346 /* No context, just make it tall enough for one row group */
347 prep->pub.pre_process_data = pre_process_data;
348 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
349 ci++, compptr++) {
350 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
351 ((j_common_ptr) cinfo, JPOOL_IMAGE,
352 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
353 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
354 (JDIMENSION) cinfo->max_v_samp_factor);
355 }
356 }
357}
358